Variability is one way to represent the data in a dataset. Variability is the measure of how spread out the data is, or how it differs from the central tendency of the data. Take for example the following dataset. This dataset is the results of flipping a coin six times and counting the number of times a head result is flipped, which was repeated 20 times.
Based on probability alone, we would expect that we would flip three heads when we flip a coin six times, since each we flip a coin there is a 50% chance of flipping a head. However, the dataset above does not show that three heads were flipped every time. The dataset does show that three is the number we got the most often, there being six instances of us getting three heads.
We can express how spread out the data is by using the different variability measures, and the most common types of variability measures are:
Standard Deviation: 1.4
While these numbers are different they are all used to communicate the same thing, how much the data is spread.